Patent Literature 1 discloses an n-type GaN with an n-type carrier of a density proportional to its oxygen concentration. The GaN is epitaxially grown on a GaAs substrate using a source gas containing oxygen. Then the GaAs substrate is removed to obtain a free-standing GaN film.
Patent Literature 2 discloses a method of forming monocrystalline gallium nitride. This method allows the doping of oxygen as an n-type dopant.
Patent Literature 3 discloses a method of fabricating a GaN based compound semiconductor. Ammonia for use in fabricating of GaN based compound semiconductor is filled in a container so that part of the ammonia is condensed into liquid. The liquid ammonia contains water at a concentration of 0.5 vol. ppm or less as measured using Fourier transform infrared spectroscopy (FT-IR). In order to form a GaN based compound layer on the substrate, a gas material containing the ammonia is introduced to a reaction chamber to which the substrate has loaded.